import React, { Component } from 'react'

export default class Count extends Component {

state = {count: 0}

increment = () => {
  const {value} = this.selectNumber
  const {count} = this.state
  this.setState({count:count+value*1})
}

decrement = () => {
  const {value} = this.selectNumber
  const {count} = this.state
  this.setState({count:count-value*1})
}

incrementIfOdd = () => {
  const {value} = this.selectNumber
  const {count} = this.state
  if(count % 2 !=0){
    this.setState({count:count+value*1})
  }
}

incrementAsync = () => {
  const {value} = this.selectNumber
  const {count} = this.state
  setTimeout(() => {
    this.setState({count:count+value*1})
  }
  , 2000)
}



  render() {
    return (
      <div>
        <h1>当前求和为：{this.state.count}</h1>
        <select ref={c => this.selectNumber = c }name="" id="">
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
          <option value="4">4</option>
          <option value="5">5</option>
        </select>&nbsp;
        <button onClick={this.increment}>+</button>&nbsp;
        <button onClick={this.decrement}>-</button>&nbsp;
        <button onClick={this.incrementIfOdd}>当前求和为基数就加</button>&nbsp;
        <button onClick={this.incrementAsync}>异步加</button>
      </div>
    )
  }
}
